This invention relates to movable magnetic head block assemblies employed in double sided flexible magnetic disk storage devices, and in particular relates to a construction thereof which allows easy, accurate and reliable position setting of the magnetic heads in relation to the rotational center of the magnetic disk.
2. Description of the Prior Art
In the current state of the information storage art, double sided flexible magnetic disk storage devices are widely used as the auxiliary or secondary storage equipment associated mainly with small scale computers. In such devices, the storage medium, the double sided flexible magnetic disk, can be removed and replaced, and accordingly to ensure uniformity and compatibility between magnetic disks recorded on the same or other machines, the positioning of the electromagnetic transducers--the heads--in relation to the rotational center of the magnetic disk, along three axes, i.e. the radial direction of the disk, the direction tangential to the tracking circumference, and the azimuth, i.e. the angle of the head gap with relation to the recording track direction, must be executed with high accuracy, consistency, and reliability.
However, in the use of a flexible magnetic disk, it has been considered desirable to apply a balanced tracking pressure on both sides of the disk at the point of contact between the transducers and the surface of the magnetic disk so that the mechanical pressure of the functional head on the magnetic disk can be counteracted to prevent the magnetic disk from being distorted thereby. For this purpose a pair of mutually opposed magnetic disk contacting surfaces which contact substantially directly opposite portions of the opposite surfaces of the magnetic disk are brought into contact with the surfaces of the magnetic disk when the same is inserted into the head block assembly for operation. Either or both of these contacting surfaces may comprise a magnetic head, whereby either or both sides of the magnetic disk may be recorded on or read from, the arrangement with heads on both sides of the disk being particularly useful in that it allows both sides of the disk to be employed alternately or continuously without having to turn the disk over. A construction employing heads on both sides of the disk is described in U.S. Pat. No. 4,089,029, dated May 9, 1978, issued to Castrodale et al, and reference may be made thereto for further details.
As described in the abovementioned patent, however, with contacting surfaces in simultaneous contact with both sides of the disk, removal of the disk would be impeded unless some arrangement were provided to temporarily retract or lift the heads away from the surface to allow unimpeded insertion or removal of the disk. This is particularly true with the most widely used type of flexible magnetic disk where the magnetic disk is permanently housed in a jacket with central holes being provided in the jacket to allow engagement between the disk drive mechanism and the disk, and with substantially parallel slots in the jacket on either side of the disk in which slots the heads move during operation. With this type of disk, unless an arrangement is provided to retract one or both of the contacting surfaces so that a gap at least greater than the greatest thickness of the jacket of the flexible magnetic disk, the contacting surfaces would foul on the jacket, causing damage to the contacting surfaces or to the flexible magnetic disk, or physically preventing the removal or insertion of the flexible magnetic disk.
Typically in the prior art the means for allowing the contacting surfaces to be retracted from the surface of the magnetic disk comprised mounting the contacting surfaces on support arms which were flexibly joined via thin cantilever springs to a carriage, such that the arms could be raised at one end, the contacting surface supporting end, either independently or, there was two arms, cooperatively together, via a suitable means of mechanical interconnection, through an arc about a point of flexure in the cantilever springs and against the pressure of those cantilever springs and any auxiliary pressure spring. The thin leaf springs were secured to the carriage by means of screws which directly clamp down the thin springs against the carriage.
The aforementioned position setting of the magnetic heads in this arrangement was carried out essentially in two stages, comprising a first stage, an approximate positioning stage, including the mounting of the magnetic heads on their respective arms, and a second stage of accurately positioning the magnetic heads in relation to the rotational center of the disk, comprising adjusting the position of the arms by loosening the screws fastening the carriage end of the cantilever springs to the support frame, adjusting the position of the arms, and hence the magnetic heads, in accordance with a test signal recorded on a setting-up magnetic disk, and then retightening the screws to secure the arms in the correct positions.
However, the torque of the screws being tightened down on the thin (typically approximately 0.1 mm thick by 20 mm wide) cantilever leaf springs while the support arm to which the other end of the spring is fixed was held in position was frequently sufficient to produce internal stresses within the cantilever springs, resulting in elastoplastic deformations of the cantilever springs which in turn caused a slight displacement of the head carrying arms supported thereby after the hold on the support arm end of the spring on released, leaving the heads in positions away from those set prior to the tightening of the screws. In practice, a method was sought to circumvent the effects of this phenomenon by anticipating this deformation-caused displacement and presetting the head carrying arms on their cantilever springs in positions offset from the ideal, correct, positions, in a direction opposite to that of the anticipated displacement that might result from the inevitable elastoplastic deformation, and by an amount equal to the estimated displacement, such that any such elastoplastic deformation induced displacement would, in theory at least, simply return the arm to the ideal, correct position. However the estimation of the elastoplastic deformation was a matter requiring considerable skill and experience, and even with these, the exercise remained a matter of trial and error, often requiring repeat operations to achieve acceptable positioning accuracy. The fact that the operation was thus one requiring great skill, and still involved the possibility of having to repeat the operation, thus made this prior method of position setting rather unsuitable for volume production.